Oil and natural gas drilling operations use copious amount of water. For example, as much as 25,000 gallons per day can be used for a single well producing natural gas or coalbed methane. In a process for separating bitumen from sand, approximately three cubic meters of water is required to produce one cubic meter of oil. Water is used primarily in water based drilling muds (WBM), which typically include fresh or salt water, a weighting agent (typically, barite or barium sulfate), clay or organic polymers, and various inorganic salts. Effluent water emanating from the drilling operations usually contain significant concentrations of both high-carbon compounds and inorganic (e.g., metal) salts. The total dissolved solids (TDS) in these waters typically range from 1 to 400 g/L. The total oil content can typically range from 40 mg/L to 2,000 mg/L.
The high-carbon compounds are those typically associated with fossil fuels, e.g., aliphatic and aromatic hydrocarbons, such as benzene, toluene, xylenes, polyaromatic hydrocarbons, petroleum fractions, diesel fractions, and organic acids containing four to nine carbon atoms. A significant portion of the high-carbon compounds enter the water stream from the fossil fuel deposit. Even higher concentrations of petroleum products (typically, diesel fuel or mineral oil) can result in the water when petroleum products are incorporated as drilling lubricants.
The metal salts emanate primarily from salts that have been included in the drilling mud or that are leached from subsurface strata. The metal salts include, for example, halides of the alkali and alkaline earth metals (e.g., NaCl, KCl, MgCl2, CaCl2), metal sulfates (particularly BaSO4), metal carbonates (e.g., Na2CO3), metal phosphates, metal nitrates, metal hydroxides, and the like. Additional metals can include arsenic, chromium, cadmium, copper, iron, lead, mercury, nickel, and zinc. In some processes, one or more compounds or materials containing these metals are intentionally added as additives to enhance the drilling process.
Due to the presence of significant levels of petroleum byproducts and metal salts, effluent water resulting from fossil fuel drilling operations is typically unfit for discharge into the environment or for re-use. Currently, no practical technologies exist for cleansing such effluent waters, and therefore, the effluent water is typically accumulated in the vicinity of the rigging operation, or stored in underground wells, or transported to a treatment facility. Storage of effluent waters typically results in the gradual seepage of the contaminants into the environment while also being costly to maintain. Transporting and subsequent treatment of the effluent waters can be prohibitively costly. More recent attempts to cleanse the effluent water on site relies on the intensive use of a non-renewable energy source, e.g., the combustion of a fossil fuel for production of electrical energy to drive a cleaning mechanism, such as reverse osmosis/membrane filtration, electrolysis, freeze-thaw methods, electrodialysis, biofiltration, and formation of hydrates.
Ion exchange is an important technology for the removal of salts and various species of metal ions from produced water. However, membrane fouling has prevented commercial application of this technology. Formation of a layer by suspended solids and colloidal matter on the membrane has been a crucial factor affecting separation of ions. Additionally, coating of the ion exchange membrane by crude oil compounds the problem. Similar problems have been observed with use of reverse osmosis.
Accordingly, there would be a benefit in a method capable of cleansing fuel processing waters of both hydrocarbon byproducts and metal salts. There would be a particular benefit in such a method which is cost efficient, and in particular, where significant cost savings result from use of renewable energy technology. There would be an additional advantage in such a method which does not require transport to a treatment facility, but which can be practiced on site. Such a method would allow fuel processing waters to be safely discharged into the environment or re-used in a cost effective manner.